Beamforming is a signal processing technique used to control the directionality of the transmission and reception of radio or sound signal. This is achieved via electronically or mechanically controlled directional antennas. A widely used class of electronically-controlled directional antennas is phased antenna array, whereby the signal at each array element is phase shifted so that the combined signal of an array at a particular angle is either constructively or destructively combined to induce spatial selectivity. By controlling the directional pattern of antennas, beamforming can improve signal quality at an intended receiver while reducing unintended interference to/from other directions. Thus beamforming has found numerous applications in radar, sonar, wireless communications, radio astronomy, and acoustics.
In particular, beamforming could be considered a key component of 5th-Generation (5G) wireless communication technology, whose operating bands include Extremely High Frequency (EHF), a.k.a. millimeter wave with high link attenuation characteristics. Radio wave propagation in EHF (30-300 GHz) is highly susceptible to absorption by objects (i.e. blockers) blocking the propagation paths. For instance, millimeter wave penetration into biological bodies is less than one to two millimeters, primarily due to high loss tangent of water, cf. for example, Om P. Gandhi and A. Riazzi, “Absorption of millimeter waves by human beings and its biological implications”, IEEE Transactions on Microwave Theory and Techniques, vol. 34, no. 2, February 1986.
With human body, it has been shown that over 90% of the incident signal power is absorbed in the skin layer, cf for example, T. Wu, et al., “The human body and millimeter-wave wireless communication systems: Interactions and implications”, IEEE International Conference on Communications (ICC), June 2015.